KB EWR 60 wire recorder - UK Vintage Radio Repair and Restoration Discussion Forum

crackle · 14th Feb 2012, 8:26 am

Hello
I have now replaced the power supply electrolytics and that cap and given the mechanicals a good clean and lubrication.
I have tested the recorder on a sample reel of wire and there is a good clear signal, of what sounds like a recording of a BBC radio Play. (I wonder if the Beeb would like a copy of it.)
The sound is clear but very quiet even with the volumn control turned up.
Is this a characteristic because of the week magnetic signal on these old wire.

The other problem is it will not successfully rewind, I have to use my finger to assist it. The drive is not slipping it just seems there seems to be not enough power in the motor, when you engage rewind the motor just slows to a stop.
The motor looks big enough to power a milk float but there is hardly any power and can easily be stopped with a finger on the shaft pulley.

Has any one any experience of these machines particularly the motor and its associated 2mf capacitor.
I have a spare rusty chassis which I have already borrowed a few spares from, it has a slightly different motor and switch on the control, with 2 capacitors a 1mf and a 2mf. Would this motor and drive be any better do you think, more power?

I have read that it is a good idea to have a second machine to rewind the wire so that you don’t cause too much wear to the head. If I cant get any more power out of the motor on the one I have just got working I may give the other chassis a good clean and try that one. The amp chassis on this one is in a shocking state and I don’t think I want to tackle getting that amp to work.
Thanks
Mike

ricard · 14th Feb 2012, 11:18 am

Unless the motor is binding (lack of lubrication, or bearing mis-alignment, it should spin freely) I would suspect the motor cap has gone bad.

crackle · 14th Feb 2012, 1:18 pm

What does the motor capacitor do, is it for power factor correction or is it an integral part of the motor mechanism for starting for instance?
Thanks
Mike

mrmagnetophon · 14th Feb 2012, 8:40 pm

Mike: Essentially even though this may be the wrong way to describe it, I like to think that a motor capacitor gives the motor the extra "umpfh" or power to start it and help it cope with tension and torque being applied to it.

ricard · 14th Feb 2012, 9:03 pm

I agree, that's a pragmatic way of describing it. It certainly behaves that way if you remove the capacitor or change its value radically.

Technically it is part of the motor design. There are essentially two coils in the motor, and the capacitor provides enough phase shift in one of the coils to provide a starting torque. Actually, it provides all the torque; an asynchronous motor is always running below its synchronous speed so the starting capacitor is always in effect.

By swapping the connections to the motor, i.e. putting the starting cap on the other coil, the direction of the motor can be reversed.

With DC motors, small value capacitors are often mounted close to the brushes to act as interference suppressors. With asynchronous motors, there are no brushes and hence no interference, electrically they are just a couple of coils.

If you operate an asynchronous motor without the starter cap, it won't start, basically there is a rotating field in the motor but its going much to fast to cause the rotor to start moving. You can manually spin the shaft and with a bit of luck it will keep rotating (if you manage to get it going fast enough, i.e. above or at its synchronous speed), but it is easily stopped.

In smaller motors its possible to introduce the phase shift by portioning off a part of the stator, and short-circuit it with a single turn of heavy gauge copper wire. This design is termed a 'shaded-pole' motor. Low to mid range tape recorders sometimes use this type of motor. It is cheaper to manufacture as only one coil is needed and no starter cap.

crackle · 15th Feb 2012, 12:18 am

Hello Guys
Thanks for your replies, Ricard that’s a useful explanation on the purpose of the motor capacitor..
The problem is solved now and I feel rather silly and too ashamed to admit what it was, but everything is working smoothly now.
Thanks again
Mike

ricard · 15th Feb 2012, 8:41 am

Hey, we've all made silly mistakes at one time or lots of times. Those that seem not to are most likely those who don't care to admit them...

Mine include turning the pinch roller screw the wrong way on a beatuiful little Dokorder miniature portable. It was left threaded so it wouldn't come off in the course of normal operation but of course I didn't realize that until I'd snapped it in two.

14th Feb 2012, 8:26 am	#1
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	KB EWR 60 wire recorder Hello I have now replaced the power supply electrolytics and that cap and given the mechanicals a good clean and lubrication. I have tested the recorder on a sample reel of wire and there is a good clear signal, of what sounds like a recording of a BBC radio Play. (I wonder if the Beeb would like a copy of it.) The sound is clear but very quiet even with the volumn control turned up. Is this a characteristic because of the week magnetic signal on these old wire. The other problem is it will not successfully rewind, I have to use my finger to assist it. The drive is not slipping it just seems there seems to be not enough power in the motor, when you engage rewind the motor just slows to a stop. The motor looks big enough to power a milk float but there is hardly any power and can easily be stopped with a finger on the shaft pulley. Has any one any experience of these machines particularly the motor and its associated 2mf capacitor. I have a spare rusty chassis which I have already borrowed a few spares from, it has a slightly different motor and switch on the control, with 2 capacitors a 1mf and a 2mf. Would this motor and drive be any better do you think, more power? I have read that it is a good idea to have a second machine to rewind the wire so that you don’t cause too much wear to the head. If I cant get any more power out of the motor on the one I have just got working I may give the other chassis a good clean and try that one. The amp chassis on this one is in a shocking state and I don’t think I want to tackle getting that amp to work. Thanks Mike

14th Feb 2012, 11:18 am	#2
ricard Octode Join Date: Mar 2006 Location: Lund, Sweden Posts: 1,632	Re: KB EWR 60 wire recorder Unless the motor is binding (lack of lubrication, or bearing mis-alignment, it should spin freely) I would suspect the motor cap has gone bad.

14th Feb 2012, 1:18 pm	#3
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: KB EWR 60 wire recorder What does the motor capacitor do, is it for power factor correction or is it an integral part of the motor mechanism for starting for instance? Thanks Mike

14th Feb 2012, 8:40 pm	#4
mrmagnetophon Retired Dormant Member Join Date: Sep 2010 Location: Ohio, USA. Posts: 757	Re: KB EWR 60 wire recorder Mike: Essentially even though this may be the wrong way to describe it, I like to think that a motor capacitor gives the motor the extra "umpfh" or power to start it and help it cope with tension and torque being applied to it.

14th Feb 2012, 9:03 pm	#5
ricard Octode Join Date: Mar 2006 Location: Lund, Sweden Posts: 1,632	Re: KB EWR 60 wire recorder I agree, that's a pragmatic way of describing it. It certainly behaves that way if you remove the capacitor or change its value radically. Technically it is part of the motor design. There are essentially two coils in the motor, and the capacitor provides enough phase shift in one of the coils to provide a starting torque. Actually, it provides all the torque; an asynchronous motor is always running below its synchronous speed so the starting capacitor is always in effect. By swapping the connections to the motor, i.e. putting the starting cap on the other coil, the direction of the motor can be reversed. With DC motors, small value capacitors are often mounted close to the brushes to act as interference suppressors. With asynchronous motors, there are no brushes and hence no interference, electrically they are just a couple of coils. If you operate an asynchronous motor without the starter cap, it won't start, basically there is a rotating field in the motor but its going much to fast to cause the rotor to start moving. You can manually spin the shaft and with a bit of luck it will keep rotating (if you manage to get it going fast enough, i.e. above or at its synchronous speed), but it is easily stopped. In smaller motors its possible to introduce the phase shift by portioning off a part of the stator, and short-circuit it with a single turn of heavy gauge copper wire. This design is termed a 'shaded-pole' motor. Low to mid range tape recorders sometimes use this type of motor. It is cheaper to manufacture as only one coil is needed and no starter cap.

15th Feb 2012, 12:18 am	#6
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: KB EWR 60 wire recorder Hello Guys Thanks for your replies, Ricard that’s a useful explanation on the purpose of the motor capacitor.. The problem is solved now and I feel rather silly and too ashamed to admit what it was, but everything is working smoothly now. Thanks again Mike

15th Feb 2012, 8:41 am	#7
ricard Octode Join Date: Mar 2006 Location: Lund, Sweden Posts: 1,632	Re: KB EWR 60 wire recorder Hey, we've all made silly mistakes at one time or lots of times. Those that seem not to are most likely those who don't care to admit them... Mine include turning the pinch roller screw the wrong way on a beatuiful little Dokorder miniature portable. It was left threaded so it wouldn't come off in the course of normal operation but of course I didn't realize that until I'd snapped it in two.